How can I create image maps with good discoverability as a map and for the regions?

I need to present a set of things in an overview / diagram form and then also individually in detail. Each thing is represented by a photo-icon in the diagram.

My worry is that the image canvas won't be recognized as a map and that it won't be apparent that each icon is clickable.

I'm not sure what to do, if I should try to use some kind of border or outline or 3D accent.